1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a plurality of high-output power semiconductor transistors.
2. Description of the Related Art
Recently, digital communication systems such as mobile communication systems using satellite and quadrature amplitude modulation (QAM) communication networks have been rapidly, developing; these communication systems require high-power microwave semiconductor devices constituted by arranging a plurality of high-frequency high-output power transistors. Accordingly to meet this requirement, for example, metal semiconductor field effect transistors (MESFETs), metal insulator semiconductor field effect transistors (MISFETs), and high electron mobility transistors (HEMTs) have been studied and developed.
In a high-power microwave amplifier using the above semiconductor devices, which are used, for example, to amplify signals of the microwave band (1 GHz to 20 GHz) for transfer to a communication satellite, the semiconductor device (semiconductor chip) is positioned between an input matching circuit and an output matching circuit, and these input and output matching circuits are used for impedance matching at the input and output sides of the semiconductor chip (semiconductor device). Further, the input side electrodes of the semiconductor chip are connected to electrodes of the input matching circuit by bonding wires, and the output side electrodes of the semiconductor chip are connected to electrodes of the output matching circuit by bonding wires. When producing (assembling) the microwave amplifier, the semiconductor chip is directly disposed at a position between the input matching circuit and the output matching circuit in a package, and the semiconductor chip is then fixed to the surface of the package by heating and melting a gold-tin alloy and by carrying out a scrub process, i.e., a process of scrubbing the semiconductor chip on the surface of the package.
Note, the semiconductor chip (semiconductor device) is made thin, e.g., 30 .mu.m or 100 .mu.m, to effectively radiate the heat self-produced by the chip, because a high-power microwave semiconductor chip produces a large amount of heat. Further, the semiconductor chip for a high-power microwave semiconductor device is made, for example, of a compound semiconductor material (Gallium Arsenide: GaAs, and the like), which is more delicate than a silicon (Si) semiconductor chip, and thus may be broken during the scrub process and the like.
Recently, semiconductor devices comprising a plurality of source electrodes, drain electrodes, and gate electrodes have been studied and developed. For example, in such a semiconductor device, the source electrodes and the drain electrodes are formed into an interdigital shape (comb-like shape), the source and drain electrodes are alternated and spaced apart from one another, and the gate electrodes are formed in a comb like manner between the source electrodes and drain electrodes.
In this semiconductor device, when the output power of the semiconductor device must be increased, the unit gate width must be widened, or a total length of the gate widths must be made larger. Accordingly, to enlarge the total gate width, the semiconductor device (semiconductor chip) is comprised of a plurality of transistor cells (semiconductor devices) arranged in parallel.
Note, when the unit gate width is widened, to thereby realize a high-frequency high-output power semiconductor device, electric power supplied to ends of the source electrodes and drain electrodes is not uniformly transmitted to the other ends of the electrodes due to the gate width, and further, an uneven phase rotation may occur, and, the output power of the semiconductor device may be lowered. Furthermore, when the number of transistor cells is increased and the cells are arranged in parallel, the shape of the semiconductor chip (semiconductor device) is a rectangle having one side much longer than the other. Namely, the semiconductor device must be made long and thin, and thus the semiconductor device may be broken during the scrub process and the like. These problems of the prior art will be explained hereafter in detail.